This invention relates to the domain of the suppression of the DC component inherent in any radio frequency chain. More particularly, the invention relates to apparatus for suppressing and possibly removing the DC component in a radio frequency reception device containing an analogue stage that processes a signal received from a digitization of this signal.
When a signal is transmitted by radio, it is generally modulated and carried by a “carrier” frequency. When the signal is received, the carrier is removed to provide a “baseband” signal. The signal is amplified and the DC component is reduced to a minimum before the signal is transmitted to the digital receiver. This type of transmission is used, for example, in the field of mobile telephony, Wi-Fi, Bluetooth and other transmissions.
FIG. 1 shows a simplified diagram of this reception. A radio frequency signal 1.1 is received by the device. It is then processed to remove the carrier by the block 1.2 which provides a baseband signal 1.3. This signal is transmitted to an analogue stage 1.4 intended to carry out an initial analogue processing on the signal. This analogue stage includes analogue components that might, exactly like block 1.2, add a DC component in the signal passing through these stages. This processing can include filtering, but often includes amplification of the signal received. This amplified signal 1.5 is then digitalized by an analog-to-digital converter 1.6, to provide a digital signal 1.7 before being transmitted for processing to a digital stage 1.8 depending on the type of device.
The different components of the analogue stages 1.2 and 1.4 are at the source of the appearance of a parasite DC component. The appearance of a DC component originates, inter alia, through the disparities of analogue components used in the construction of differential stages. The stages carrying out amplification functions should naturally be painstakingly elaborated to avoid successive amplifications of the DC component saturating the analog-to-digital converter downstream of the analogue chain. Such a component, even if with a low range, will continue to subsist regardless.
In practical terms, it can be observed that, without processing, these DC components can saturate amplification stages and the converter.
It is therefore indispensable to offer a processing system to remove all or part of the effect caused by these DC components before the converter.
It is known to carry out in a steady state, a retroactive low-pass filter loop to provide compensation at a single point of the analogue chain. This method raises the Issue that if the compensation point is at the end of the analogue chain, it is still possible for a previous amplification stage to be saturated. On the other hand, the DC component to be corrected is amplified by all the amplification stages and can be significant at this level. If the number of amplifiers of the chain increases, a single compensation point can turn out to be insufficient to avoid saturation upstream and downstream of this point.